Effect of norepinephrine and phenylephrine on prothrombotic response in patients undergoing cesarean section under spinal anesthesia: protocol for a randomized, double-blind, controlled study

Background Norepinephrine and phenylephrine are commonly used vasoactive drugs to treat hypotension during the perioperative period. The increased release of endogenous norepinephrine elicits prothrombotic changes, while parturients are generally in a hypercoagulable state. Therefore, this trial aims to investigate whether there is a disparity between equivalent doses of prophylactic norepinephrine infusion and phenylephrine infusion on prothrombotic response in patients undergoing cesarean section under spinal anesthesia. Methods Sixty-six eligible parturients will be recruited for this trial and randomly assigned to the norepinephrine or phenylephrine group. The “study drug” will be administered at a rate of 15 ml/h starting from the intrathecal injection. The primary outcome are plasma coagulation factor VIII activity (FVIII: C), fibrinogen, and D-dimer levels. The secondary outcomes include hemodynamic variables and umbilical artery blood pH value. Discussion Our study is the first trial comparing the effect of norepinephrine and phenylephrine on prothrombotic response in patients undergoing cesarean section under spinal anesthesia. Positive or negative results will all help us better understand the impact of vasoactive drugs on patients. If there are any differences, this trial will provide new evidence for maternal choice of vasoactive medications in the perioperative period. Trial registration Chinese Clinical Trial Registry ChiCTR2300077164. Registered on 1 November 2023. https://www.chictr.org.cn/. Supplementary Information The online version contains supplementary material available at 10.1186/s13063-024-08255-x.


Background and rationale {6a}
Spinal anesthesia promotes systemic vasodilation in patients, which inevitably leads to a redistribution of blood between the core and periphery, and resulting in hypotension.Norepinephrine and phenylephrine are commonly used vasoactive drugs in patients undergoing cesarean section [1][2][3].Numerous studies have compared the regulatory effects of norepinephrine and phenylephrine on perioperative hypotension in patients undergoing cesarean section [3,4], as well as fetal outcomes [5,6].As a type of α-agonist, phenylephrine is a powerful and rapidly acting vasopressor that can better maintain the acid-base status of the fetus and has replaced ephedrine as the preferred vasopressor for hypotension during cesarean section [7].However, phenylephrine is more prone to reflex bradycardia and decrease cardiac output [8].Norepinephrine acts as an α-adrenergic agonist and also has a weak β-agonist effect, which has been the frequently used drug for treating hypotension undergoing cesarean section [9][10][11].
The coagulation system undergoes physiological changes to reach a hypercoagulable state to prevent severe bleeding during delivery [12].Most of the pregnant patients who experienced acute coronary syndrome (ACS) had no coronary artery disease before, and the pathological mechanism involved was mainly non-atherosclerosis [13].Meanwhile, the formation of blood clots plays an extremely important role in ACS [14].Research has confirmed that the release of norepinephrine promotes blood clotting, and the resulting prethrombotic state may be a vital mechanism for triggering acute coronary artery disease [15].However, whether norepinephrine and phenylephrine trigger coagulation changes measured in a laboratory setting and predict the risk of cardiovascular diseases (CVD) has not previously been investigated.The main coagulation molecules selected in this trial include FVIII: C, fibrinogen, and D-dimer, which have been shown to be closely associated with the risk of CVD [16][17][18].The aim of this trial is to compare the prothrombin response of norepinephrine and phenylephrine.

Objectives {7}
The aim of this trial is to compare the prothrombin response of prophylactic infusion of the equivalent dose of norepinephrine and phenylephrine in patients undergoing cesarean section under spinal anesthesia.This study will provide a new theoretical basis for exploring the administration of vasoactive drugs in patients with hypercoagulation state during the perioperative period.

Trial design {8}
This study is a two-arm randomized controlled trial (RCT) with a 1:1 allocation ratio and explores the superiority of two interventions on patients' prothrombotic response.The intervention will be implemented according to the protocol, with independent researchers conducting and monitoring randomization.Figure 1 shows the Consolidated Standard flow chart for reporting trials.

Study setting {9}
This trial plans to recruit patients scheduled to undergo cesarean section, with an age range of 18-40 years.Eligible subjects will be recruited at the Second People's Hospital of Hefei, a large tertiary hospital in China that performs thousands of cesarean sections each year.Blood samples will be sent to the Key Laboratory of Anesthesiology and Perioperative Medicine of Anhui Higher Education Institutions, Anhui Medical University, for coagulation function testing.Figure 2 is a Standard Protocol Items [19].
(2) The patient fails to complete data collection.
(3) Adverse events occur and require treatment.
(4) The subject's pathological and physiological changes require withdrawal.(5) The researcher believes that the patient is not suitable to continue.

Information consent {26a}
Elective cesarean sections are performed by an anesthetist who visits the patients the day before the operation to recruit the patient and obtain informed consent.
For emergency cesarean sections, informed consent can be signed in the operating theater, prior to anesthesia.Patients can withdraw at any time.Not participating in this trial will not affect the right of parturient to receive routine anesthesia and surgery.

Additional consent provisions for collection and use of participant data and biological specimens {26b}
When signing the informed consent form, participants will be asked if they are willing to donate blood and fetal umbilical artery blood samples, and only patients who agree will be enrolled.Blood samples left over from testing will be destroyed.

Explanation for the choice of comparators {6b}
Norepinephrine group: Norepinephrine will be pumped intraoperatively.Phenylephrine group: Phenylephrine will be pumped during the operation.Norepinephrine and phenylephrine are both vasoactive drugs commonly used in clinical practice, and their use will be beneficial in maintaining the stability of maternal intraoperative circulation.

Intervention description {11a}
Patients who met the inclusion criteria will be recruited until 66 cases.Phenylephrine (100 µg/ml) and norepinephrine (8 µg/ml) will be prepared by assistants who are not involved in this trial.Patients undergo routine vital sign monitoring after entering the operating room.Intravenous access will be secured using an 18G intravenous catheter.Within 15 min before surgery, a rapid intravenous infusion of 5 ml/kg lactate Ringer solution will be administered, and then continue the infusion at a rate of 6 ml/kg/h.The ambient temperature in the operating room is maintained at 22-24 °C.Spinal anesthesia will be implemented using 0.75% ropivacaine hydrochloride 12 mg at the L 2 -L 3 or L 3 -L 4 intervertebral space in a lateral decubitus.The parturient maintains a supine position on the left side at 15 degrees to displace the uterus to the left.The "study drug" will be administered at a speed of 15 ml/h starting with the intrathecal injection.Administration of the "study drug" ends at the beginning of suturing the skin.The plane of midline sensory blockade will be check by pin prick with blunt tipped needle, and the maximum sensory plane is generally reached within 20 min after spinal blockade.
Circulatory parameters should be conducted every 3 min within the first 15 min after anesthesia.Ephedrine 6 mg should be used for treatment hypotension when the systolic blood pressure is below 90 mmHg.Hypertension is an increase in mean arterial pressure (MAP) > 20% from baseline.Once hypertension occurs, medication infusion should be stopped immediately until MAP returns to below the hypertension.Atropine 0.5 mg can be used for bradycardia (heart rate < 60 beats/min) treatment.

Criteria for discontinuing or modifying allocated interventions {11b}
Interventions will likely be interrupted or modified in the event of adverse events, serious procedural errors, or voluntary patient withdrawal.

Strategies to improve adherence to interventions {11c}
During the informed consent process, patients will be informed of the importance, potential benefits, and possible risks of participating in this study.There will be no additional financial burden associated with the study, and abnormalities in coagulation parameters will be promptly communicated and treated.

Relevant concomitant care permitted or prohibited during the trial {11d}
No concomitant care is prohibited during the trial.

Provisions for post-trial care {30}
Patients will be informed if they have a postoperative coagulation abnormality, and will be reviewed and treated.If there are significant abnormalities in the perioperative data of patients, repeated measurements and analysis should be carried out immediately.The obtained data will be verified by two people and input into the computer.

Participant timeline {13}
Blood samples will be taken at two time points, entering the operating theater and suturing the skin, to determine levels of FVIII: C, fibrinogen, and D-dimer.

Recruitment {15}
Sixty-six patients with confirmed full-term pregnancies in the Department of Obstetrics of the Second People's Hospital of Hefei City will be recruited into one of the groups if they are eligible and the medical staff will inform them of the benefits and risks of the study, and the patients will voluntarily take part in this trial after being fully informed.The Second People's Hospital of Hefei is a large tertiary hospital in China, where thousands of cesarean sections are performed annually.Recruitment of the first participant took place in October 2023 and is expected to be completed by the end of 2024.

Sequence generation {16a}
Subjects will be randomly assigned to receive a phenylephrine or norepinephrine infusion in a 1:1 ratio by a statistical expert using SPSS V.16.0 software.

Concealment mechanism {16b}
Sheets of paper will be labeled with grouping information and placed in sequentially numbered envelopes.

Implementation {16c}
Patient recruitment will be carried out by the anesthetist and drugs will be dispensed by a nurse not involved in this study.

Assignment of interventions: blinding Who will be blinded {17a}
Neither the patient nor the anesthetist will be aware of the grouping.

Procedure for unblinding if needed {17b}
Patients will be allowed to be unblinded if they have a serious adverse reaction or the trial ends.

Plans for assessment and collection of outcomes {18a}
Preoperative visitors screen enrolled patients and collect informed consent forms.Anesthesiologists will record the primary and secondary outcomes in the case report form (CRF).All CRF will be stored in a locked drawer.All information will be stored on a computer with a password.This trial will also be monitored by two clinical doctors for safety.

Plans to promote participant retention and complete follow-up {18b}
Our team has completed several clinical studies of these patients in advance and is experienced in dealing with recruitment and dislodgement.Considering that thousands of cesarean sections are performed each year, this means that data collection will be completed within 2024.

Data management {19}
Patient data collected by the researcher will be stored in a locked cabinet and electronic files will be kept in a computer with a password.

Confidentiality {27}
Information collected during the course of the research will be in a re-identifiable form and no information generated by this project may be used for any other purpose.Only study investigators will have access to study information.

Plans for collection, laboratory evaluation, and storage of biological specimens for genetic or molecular analysis in this trial/future use {33}
The patient's venous blood will be drawn into a sodium citrate tube containing 3.8% phosphate.The sample will be centrifuged at room temperature (2000 g, 20 min) to obtain plasma, which will be transferred to polypropylene Eppendorf tubes and stored at − 80 °C until measurement in the Laboratory of Anesthesiology and Perioperative Medicine of Anhui Higher Education Institutes, Anhui Medical University.FVIII: C (pg/ml), fibrinogen (g/l), and D-dimer levels (mg/l) are measured using the enzymelinked immunosorbent assay.

Statistical methods for primary and secondary outcomes {20a}
Our data will be analyzed using SPSS 14 software (USA).The Kolmogorov-Smirnov test will be used to test the normality of the data distribution, and all data will be evaluated for linearity using scatter plots.Normally distributed data will be expressed as the mean with a 95% confidence interval (95% CI) and analyzed by parametric testing (paired t-test).Non-normal distribution parameters will be expressed as median and range.A nonparametric test (Wilcoxon test) was used for analysis.Discrete variables will be analyzed using unpaired Student t-test or Mann-Whitney U test for parametric or non-parametric data.An independent t-test will compare the two groups' coagulation molecule values.The condition for the significant difference is a P value < 0.05.

Interim analyses {21b}
After the first 30 participants have completed data collection, an interim analysis will be performed and the trial will be terminated if patients in the norepinephrine group have lower coagulation indices than those in the phenylephrine group.

Methods for additional analyses (e.g., subgroup analyses) {20b}
Due to the small sample size and homogeneous gender, no additional analyses beyond the primary and secondary outcome were considered for this study.

Methods in analysis to handle protocol non-adherence and any statistical methods to handle missing data {20c}
Missing data from participants who failed to complete the entire study will not be included in the statistics.

Plans to give access to the full protocol, participant-level data, and statistical code {31c}
This study protocol anonymized participant datasets are available to other researchers on request.

Composition of the coordinating center and trial steering committee {5d}
The clinical study was arranged in the Second People's Hospital of Hefei, and all coagulation indices were monitored in the laboratory of the Department of Anesthesiology of the Second Affiliated Hospital of Anhui Medical University.

Composition of the data monitoring committee, its role, and reporting structure {21a}
As this randomized controlled exercise trial is not a large, complex, or high-risk clinical trial, we do not consider the DMC setting to be necessary.

Adverse event reporting and harms {22}
Theoretically, extravasation of norepinephrine can cause local ischemia, and the concentrations in this study have been shown to be safe.In the event of an adverse event, it will be recorded and reported to the hospital ethics committee.

Frequency and plans for auditing trial conduct {23}
The trial will be audited by investigators from the Clinical Trial Office of the Second Affiliated Hospital of Anhui Medical University and the Second People's Hospital of Hefei.They will conduct on-site or remote monitoring in accordance with Good Clinical Practice (GCP) and national regulations.

Plans for communicating important protocol amendments to relevant parties (e.g., trial participants, ethical committees) {25}
This trial will be conducted strictly in accordance with the protocol (version 1.0).Once modifications occur, the revised protocol will be formally submitted to the relevant ethics trial registration authorities.It will also be resubmitted with amendments to the study protocol to Trials.All participants must provide informed written consent before they can take part in the study.

Dissemination plans {31a}
The results of this trial will be submitted and disseminated in the form of a manuscript to the journal for review and publication.Patients with coagulation abnormalities will be informed and given further investigations, assessment, and treatment.

Discussion
The peripheral vasoconstriction caused by the administration of vasoactive drugs is characterized by a decrease in the redistribution of blood volume from the core to the periphery, thereby maintaining stable blood pressure [20].Combined with liquid therapy, phenylephrine has been widely used in the prevention and treatment of hypotension in patients undergoing cesarean section [21,22].Even in cesarean section surgery for severe preeclampsia, phenylephrine can be safely used in reduced doses [23].Norepinephrine is equally effective in treating hypotension during spinal anesthesia as fixed rate infusion and can avoid bradycardia caused by phenylephrine and favorable acid-base distribution in newborns due to the norepinephrine's β effectively maintaining placental blood flow [24].In a word, norepinephrine can safely and effectively maintain maternal hemodynamics without causing adverse events to pregnant women or fetuses [25,26].
CVD is common among women of childbearing age, which has become the main reason for the increased morbidity and mortality of pregnant women [27,28].The prothrombotic state is a critical cause of acute coronary artery disease, and blood hypercoagulable is believed to be associated with increased release of endogenous norepinephrine [15,29].In the study, we will investigate the prothrombotic response, which may be differences due to infusion of norepinephrine and phenylephrine.
In this study, unlike previous single doses of norepinephrine and phenylephrine, we used a continuous measured infusion, which allowed tighter control of blood pressure, reduced hemodynamic fluctuations, and minimized anesthetist intervention [27].The design of this study was to administer vasoactive drugs through a peripheral vein, in contrast to the prevailing view that vasoconstrictors must be administered via a central venous catheter.A retrospective cohort study evaluated the risk of adverse reactions [28], including skin necrosis, associated with receiving a peripheral intravenous infusion (20 µg/ml) of norepinephrine through a database.The results found that of 14,385 patients receiving peripheral continuous infusion of norepinephrine, only 5 patients experienced extravasation of the drug and did not require surgical or medical intervention, concluding that there was no significant association between peripheral intravenous norepinephrine infusion and adverse events.Peripheral administration of norepinephrine is recommended [29]: through a large proximal vein or anterior elbow fossa vein at a concentration not exceeding 32 μg/ml, for a duration not exceeding 12 h, with the infusion site observed every 2 h and an emergency plan in place.In this study, we will configure 8 µg/ml of norepinephrine and the whole procedure will take about 1 h.For safety reasons, we will observe the infusion location once in half an hour and have phentolamine or nitroglycerin on hand to deal with injuries caused by drug extravasation.
Considering that the central norepinephrine projection system is central to fear and anxiety [30] the patient's preoperative anxiety and fear may have an impact on the release of norepinephrine.Although we will not assess the patient's level of anxiety due to personnel limitations, we will give the patients a comprehensive understanding of the entire surgical process before surgery and meet their requirements as much as possible to minimize the interference of the patient's possible anxiety on the indicators.

Trial status
The trial is ongoing and recruiting.The protocol (version 1.0) was approved on November 1, 2023.Patient recruitment begins in November 2023 and is expected to be completed before December 2024.

Fig. 2
Fig. 2 SPIRIT figure-schedule of enrolment, interventions, and assessments.SPIRIT, Standard Protocol Items: Recommendations for Interventional Trials